Brake shoe mold



F. M. POE

June 6, 1933.

Filed May 22, 1931 l atented June 1933 UNITED STATES FRED M. POE, F SUFFERN, NEW YORK, ASSIGNOR TO THE AMERICAN BRAKE SHOE AND FOUNDRY COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION DELA- maximum wear PATENT? OFFICE WARE BRAKE SHOE MOLD Application filed May 22,

This invention relates to molds for use in the manufacture of cast iron brake shoes from chilling cast iron. A cast iron of comparatively high chilling property is used to give V but it is essential that the metal of the shoe be gray in structure to give the maximum strength and friction. According to the present practice these shoes are made in sand molds which are satisfactory so far as the product is concerned but are open to theobjection that they can only be used once and are destroyed at the conclusion of each casting operation.

Itis the object of my invention to provide a permanent or semi-permanent brake shoe mold which can be used for repetition casting operations to produce a brake shoe having a gray structure from cast iron of high chilland have a gray ing property.

A further object of the invention is to provide a brake shoe mold adapted to receive molten high chilling cast iron to produce brake shoes of equal quality to but at considerably lower cost than brake shoes now produced in sand molds.

As the result of long experience in the art of brake shoe manufacture and careful research and study relating to metal casting operations and the method and means used therein, with particular reference to their applicability to casting brake shoes, I find that two important factors must be observed. First, the cast metal must be gray and not show any chill; and, second, the mold structure about the mold cavity must not be damaged when the molten metal is poured against it. If the metal in the shoe shows a chill where it is desired that it should be unchilled structure, the shoe will be brittle, break easily, and fail to give the desired friction; and if the wall of the mold cavity cracks or spalls it will not be serviceable or satisfactory. Low

thermal conductivity is necessary to prevent the casting from chilling but heat insulating materials as a usual thing are soft and friable in character and will not stand up against molten cast iron poured against them. Any material that is sufficiently hard and dense to stand up against the molten iron has such a high ther- 1931. Serial No. 539,165.

mal conductivity and conducts the heat away so rapidly that the iron cast against it is chilled. Various materials have been pro posed and some have been used but to the best of my knowledge none of them has ever proved to be satisfactory in commercial operations. l i

I have discovered that in order to produce abrake shoe of suitable character in a permanent or semi-permanent mold it is essential that the mold cavitybe formed in a material having a thermal conductivity not to exceed 20 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and having low coefficient of expansion not to exceed .0000006 at 1100 centigrade.

In present foundry practice with sand molds it is customary to embed a cast iron chill block in the wall of the mold cavity where it is desired to give the brake shoe a white structure and while such a chill block may be satisfactorily used with my invention, I prefer to use a non-metallic material which should have a thermal conductivity in excess if 90 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and with coefficient of expansion not to exceed.0000050 per degree from 200 to 900 centigrade.

My invention consists of a brake shoe mold having a mold cavity formed in an inert base non-metallic material with low heat conduc tivity not to exceed 20 B. t. u. per hour per square foot per degree difference Fahrencentigrade to permit repeated casting operations with a chilling iron and producing un chilled brake shoes; and, if it is desired to provide the brake shoe with a white structure in some part or parts, my invention further consists in providing the corresponding part or parts of the mold cavity in a base material of comp aratively high heat conductivity in excess of 90 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and low coefiicient of expansion not to exceed .0000050 per de ree from 200 to 900 centigrade such as si icon car to form the shoe 8,

bide, so that a part or parts of the shoes produced will have a white structure corresponding with the chilled parts of shoes formed in sand molds provided with chilled blocks.

For the inert base non-metallic material I prefer to use a thoroughly comminuted mixture of crushed fused silica with a suitable bonding material such as clay. These materials are thoroughly mixed and formed into shapes providing a mold cavity of proper size and design and the shapes are pressed, baked and burned at the pressure and temperature suitable to form a mold. While I prefer to use fused silica as the base material and clay as the bonding material, I may use any equivalent materials within the scope of my invention and meeting the requirements thereof as to heat conductivity and coefficient of expansion. For the chilling part or parts in the mold cavity I prefer to use a block or blocks of metal or inert base non-metallic material of comparatively high heat conductivity and low coeflicient of expansion.

I have illustrated'in a simple form in the accompanying drawing a mold embodying my invention. This mold consists entirely of the materials which I have described and this I consider to be sufficient illustration of the invention, but it will be understood that the mold may be enclosed or supported in a suitable frame to protect it and to facilitate the use thereof in general foundry operations. Referring to the drawing Fig. 1 is a longitudinal sectional View of the mold on the line 11 of Fig. 2; and

Fig. 2 is a transverse sectional View on the line 2-2 of Fig. l.

The mold comprises a drag arranged to fit properly one upon the other and having a mold cavity 5 and a pouring gate 6. The mold cavity may be made in any size and design desired and the pouring gate will be made in any manner and located in any place suitable for the purpose. Chill blocks 7 are shown embedded in the drag at the ends of the mold cavity to produce a white structure in the end portions of the shoe, but if this white structure is not desired the chill blocks will be omitted and the drag will be formed completely of the nonchilling material; The chill blocks may be made of metal or of an inert base non-metallic material having thermal conductivity in excess of 90 B. t. u. per hour per square foot per degree diiference Fahrenheit per inch thickness and with coefficient of expansion not to exceed .0000050 per degree from 200 to 900 centigrade.

The molten metal is poured through the gate 6 into the cavity 5 and fills the cavity after which the cope is lifted from the drag and the shoe is withdrawn from the mold cavity in the drag and the sprue 9 is removed from the'shoe. A re- 3 and a cope l enforce back 10 of any kind may be supported in the mold cavity to be embedded in the shoe during the casting operation and a lug strap 11 and core 12 are also supported in the mold cavity in the cope to form the attaching lug 13. lVith my invention I am able to use cast iron of comparatively high chilling property and produce a shoe in which the cast iron part is of uniform gray structure which will give maximum strength and friction. Repeated casting operations may be performed without damaging the walls of the mold cavity and this materially reduces the cost of manufacture.

I claim:

1. A brake shoe mold having a mold cavity with walls formed of a compound consisting of an inert base non-metallic material and a bonding material, said walls having a thermal conductivity not to exceed 20 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and with low coeficient of expansion not to exceed .0000006 at l100 centigrade.

2. A brake shoe mold having a mold cavity with Walls formed of an inert non-metallic material including a base of crushed fused silica and a non-metallic bond.

3. A brake shoe mold having a mold cavity with walls formed in part of a compound consisting of an inert base non-metallic material and a bonding material, said walls having a thermal conductivity not to exceed 20 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and with low coefiicient of expansion not to exceed .0000006 at 1100 centigrade and in part of metallic material.

4. A brake shoe mold having a mold cavity with walls formed in part of an inert base A non-metallic material having a thermal conductivity not to exceed 20 B. t. u. per hour per square foot per degree difference Fahrenheit per inch thickness and with low c0efficient of expansion not to exceed .0000006 at l100 centigrade and also formed in part of an inert base non-metallic material having a thermal conductivity in excess of 90 B. t. u. per hour per square foot per degree dilference Fahrenheit per inch thickness and with coefficient of expansion not to exceed .0000050 per degree from 200 to 900 centigrade.

FRED M. POE. 

